Freethought & Rationalism Archive

secular-knight 69 · 03-31-2003, 11:52 AM

From my very limited knowledge, most genetic variability is with in race as opposed to across race.

I understand the concept, but how can it be?

ps418 · 03-31-2003, 12:01 PM

Quote:

Originally posted by secular-knight 69
From my very limited knowledge, most genetic variability is with in race as opposed to across race.

I understand the concept, but how can it be?

Most alleles occur within all races. Only a few percent of alleles are population-specific. All thats needed for this to happen is maintenance of some gene-flow between populations, so that a variant arising in one population can travel the world.

Patrick

lpetrich · 03-31-2003, 06:14 PM

Alternatively, our species is descended from a single, well-mixed population that has not had enough time to accumulate very much genetic divergence.

This is consistent with the Mayr/Gould conception of speciation as occurring in relatively small populations that are offshoots of the ancestral populations.

Diffusion distance is easy to estimate with the hypothesis that genes do random walks:

(diffusion distance) ~ (individual's typical total travel distance)*sqrt((total time)/(generation time))

Gene diffusion in our species over the last 30,000 years (1000 generations) would go for a distance of only 30 * (individual travel distance), and diffusion over a distance of 10,000 km requires a travel distance of 300 km.

Thus, massive migrations would be necessary for keeping genes well-mixed.

secular-knight 69 · 04-01-2003, 11:44 PM

Is it a matter of something like this:

We have group A, B, and C. These groups share 90% of the same genes.

These groups have subgroups that have some different genes.

So, when if we pick a random member from any group their genes will be 90% the same.

With the subgoups being smaller the different genes are more prevalent?

Example:

The entire population was genes for legs, 2 arms, and this would be the norm for the whole species, but subspecies might have genes a differences between the length of arms in group like A that might have arm lengths between 1 and 2 meters.

The whole popultion has two arms, so they share that in common; however, the in group variation is bigger in group A than the others.

Does that make sense to you?

echidna · 04-01-2003, 11:51 PM

SK69, not answering your question directly, but an earlier thread touched on this topic & never had time to post this link. You may find it interesting.

The reality of race

Quote:

Race doesn't exist, the mantra went. The DNA inside people with different complexions and hair textures is 99.9 percent alike, so the notion of race had no meaning in science. At a National Human Genome Research Institute (NHGRI) meeting five years ago, geneticists were all nodding in agreement. Then sociologist Troy Duster pulled a forensics paper out of his briefcase. It claimed that criminologists could find out whether a suspect was Caucasian, Afro-Caribbean or Asian Indian merely by analyzing three sections of DNA.

Quote:

But genetics cannot prove that race doesn't exist, Duster explains. No amount of logic will erase the concept or destroy the disparities that arise from it, because people use race to sort their social groupings and to define their social and economic interactions. Moreover, they do so in ways that have significant biological consequences. Duster recently helped to draft a 15-page statement for the American Sociological Association showing how race persists as a factor in disparities in health and other areas of life. "You cannot just get rid of the concept without doing tremendous damage to the epidemiologic research done so far," Duster says. African-Americans are three times as likely to die from heart disease, for example. "Blacks are redlined by banks, followed by department store security, pulled over by the police. This can produce hypertension," he points out. "It can give you a heart attack."

Wounded King · 04-02-2003, 12:46 AM

It is obviously true the the concept of Race exists and cannot be abolished overnight. The important question is how relevant is the social construct "Race" to biology and the study of genetic variation within and between populations. If so what is required to constitute a race? Are people with blue eyes a different race from those with Brown?

To quote the quote

Quote:

It claimed that criminologists could find out whether a suspect was Caucasian, Afro-Caribbean or Asian Indian merely by analyzing three sections of DNA.

This doesnt mean that the concept of race is suddenly biologically relevant, simply that it is possible to ditinguish between populations based on certain criteria. One could similarly distinguish amongst almost any group of populations with reasonably distinct evolutionary histories provided one identified the right sections of DNA

I found Secular knights original post a bit vague. Are these variations between people of different races living in the same population or between a caucasian population in eastern europe and a tribe of Kalahari Bushmen?

ps418 · 04-02-2003, 06:13 AM

The article by Risch et al that I posted a few days ago explains clearly one important aspect of the biological relevance of between-race genetic differences -- different distributions of SNPs between races, for instance, especially low-frequency SNPS, are likely to be responsible for many of the observed variations in response to therapeutic drugs (e.g. due to drug-metabolizing enzyme (DME) polymorphisms) (see Wilson et al, 2001), as well as the observed differential susceptibilities to various diseases such as hypertension. The idea is that to the extent that self-reported ancestry is genetically-informative, it can be useful in making the best treatment decisions.

Quote:

It is likely that genetic differentiation among races is enhanced for disease-predisposing alleles because such alleles tend to be in the lower frequency range. It is well known that rarer alleles are subject to greater fluctuation in frequency due to genetic drift than common alleles. Indeed, for most Mendelian diseases, even higher frequency alleles are found only in specific races (for example, cystic fibrosis and hemochromatosis in Caucasians). Furthermore, recent SNP surveys of the different races have shown that lower frequency variants are much more likely to be specific to a single race or shared by only two races than are common variants [12,19-20]. In one study, only 21% of 3,899 SNPswere found to be pan-ethnic, and some race-specific SNPs were found to have a frequency greater than 25% [12].

Risch et al., 2002. Categorization of humans in biomedical research: genes, race and disease. Genome Biology 3(7):comment2007.1-2007.12 . PDF

Wilson et al., 2001. Population genetic structure of variable
drug response. Nature Genetics 29:265-269.

Patrick

tronvillain · 04-02-2003, 01:40 PM

This was one of the things my search turned up:

Quote:

Despite our visual perception of the variation between races, studies have shown that as much as 85% of all human variation occurs between individuals of the same population while less than 10% of the variation was between the major races - represented in the broadest sense by Africans, Asians and Europeans. This pattern of diversity is largely accounted for by human evolutionary history. Studies of human DNA from populations around the world suggests a common African ancestry living some 200,000 years ago. Modern theories of human evolution suggest that expansion of populations from Africa began 100,000 years ago - giving nearly twice as much time for variation to accumulate in sub-Saharan Africa as in the rest of the world, writes Disotell.

This appears to be exactly what secular-knight 69 was talking about, and as far as I can tell it does not eliminate the concept of "race." I may be crazy, but what it seems to me to be saying that only ten percent of the variation between two individuals of different races could be accounted for by them being different races, and that the rest of the variation would be independent of race.

secular-knight 69 · 04-02-2003, 09:53 PM

Quote:

only ten percent of the variation between two individuals of different races could be accounted for by them being different races, and that the rest of the variation would be independent of race.

tronvillain

If your reading of it is correct then than is an explaination that makes sense to me. Thanks for the insight.

03-31-2003, 11:52 AM	#1
secular-knight 69 Junior Member Join Date: Mar 2003 Location: In a black man's body Posts: 23	Genetic Variability From my very limited knowledge, most genetic variability is with in race as opposed to across race. I understand the concept, but how can it be?

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03-31-2003, 06:14 PM	#3
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	Alternatively, our species is descended from a single, well-mixed population that has not had enough time to accumulate very much genetic divergence. This is consistent with the Mayr/Gould conception of speciation as occurring in relatively small populations that are offshoots of the ancestral populations. Diffusion distance is easy to estimate with the hypothesis that genes do random walks: (diffusion distance) ~ (individual's typical total travel distance)sqrt((total time)/(generation time)) Gene diffusion in our species over the last 30,000 years (1000 generations) would go for a distance of only 30 (individual travel distance), and diffusion over a distance of 10,000 km requires a travel distance of 300 km. Thus, massive migrations would be necessary for keeping genes well-mixed.

04-01-2003, 11:44 PM	#4
secular-knight 69 Junior Member Join Date: Mar 2003 Location: In a black man's body Posts: 23	Is it a matter of something like this: We have group A, B, and C. These groups share 90% of the same genes. These groups have subgroups that have some different genes. So, when if we pick a random member from any group their genes will be 90% the same. With the subgoups being smaller the different genes are more prevalent? Example: The entire population was genes for legs, 2 arms, and this would be the norm for the whole species, but subspecies might have genes a differences between the length of arms in group like A that might have arm lengths between 1 and 2 meters. The whole popultion has two arms, so they share that in common; however, the in group variation is bigger in group A than the others. Does that make sense to you?

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